04/19/23 IENG 475: Computer-Controlled Manufacturing Systems

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IENG 475 - Lecture 08

Group Technology –

Parts Classification & Coding (PC & C)

04/19/23 IENG 475: Computer-Controlled Manufacturing Systems

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Assignment HW 01

• Download HW 03 from the Schedule page• Use the copies of the Opitz & Vuosa-Praha GT codes to

classify and code the part on HW

• Turn in HW 03 at the start of the next class!

04/19/23 IENG 475: Computer-Controlled Manufacturing Systems

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Group Technology (GT)

Philosophy:• Use the similarity of current products to simplify the

design and manufacturing of new products Some Applications:

• Identify and reuse similar process plans

• Identify and reuse similar CNC programs

• Identify the equipment that may be best used in a particular machine cell

• Identify and eliminate redundant inventory Requirement:

• A taxonomy of part characteristics

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Benefits of GT Facilitates formation of part

families and machine cells Quick retrieval of designs,

drawings, & process plans Reduces design duplication Provides reliable workpiece

statistics Facilitates accurate estimation of

machine tool requirements and logical machine loadings

Permits rationalization of tooling setups, reduces setup time, and reduces production throughput time

Allows rationalization and improvement in tool design

Aids production planning and scheduling procedures

Improves cost estimation and facilitates cost accounting procedures

Provides for better machine tool utilization and better use of tools, fixtures, & people

Facilitates NC part programming.

(Ham)

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How to Identify Groups Similar Design Attributes

• Size of parts

• Geometric shape of parts

• Materials

• Technique: Parts Classification & Coding

Similar Manufacturing Attributes• Common processing steps (routings)

• Common tools and fixtures

• Technique: Production Flow Analysis

Similarity groupings are called Part Families

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Parts Classification & Coding

Group Technology applied to parts is called Parts Classification & Coding (PC&C)

Methods:• (Human) Visual Inspection

• Least sophisticated

• Least accurate (repeatable)

• Least expensive

• (Computer) Feature Recognition

• Most expensive to develop

• Most accurate (repeatable)

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Typical PC&C Attributes Part Design Attributes:

• Basic external shape

• Basic internal shape

• Major dimensions

• Length/diameter ratio

• Minor dimensions

• Material type

• Tolerances

• Surface finish

• Part function

(Groover)

Part Mfg Attributes:• Major process

• Minor operations

• Major dimension

• Length/diameter ratio

• Operation sequence

• Surface finish

• Machine tool

• Production time

• Batch size

• Annual production

• Required Fixtures

• Cutting tools

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PC&C Code Types

Three PC&C Code Types:• Hierarchical (monocode)

• Succeeding position code values depend on the preceding code values

• Very detailed & compact, but complex

• Tend to exaggerate minor differences

• Chain (polycode)

• Individual code values do not depend on the other code positions

• Robust (least affected by minor differences)

• Least compact for same level of detail (30+ digits)

• Hybrid

• Mixture of hierarchical and chain types

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GT PC&C Code Examples Vuosa-Praha

• 4 digits (monocode) Opitz

• Basic - 5 digits (monocode)

• Enhanced - 9 digits (hybrid) DCLASS

• 8 digits (monocode) MICLASS

• 12 digits (polycode) KK-3

• 21 digits (hybrid)

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GT PC&C Code Example

Construct the specified GT codes for the following part, initially made from a nodular graphitic (grey iron) casting. Support your answer on each digit for credit. Note: Below the axis is an interior section view, above is the un-sectioned exterior view.

Milled Locating Groove

Axis Through Hole Pilot 10.50 mm

Ø 75 ± .0254 mm

187.50 mm

Radius 0.0254 mm on Spur Gear Roots and Crests

M 12 Interior Thread Along Axis

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CAPP Computer-Aided Process Planning

• Requires a pre-existing GT coding Two Methods:

• Variant• Retrieve a process plan for a similar part

• Modify the process plan adapting it to the new part• New part process plan is a variation on the family STANDARD

process plan

• Generative• Based on the new part’s attributes, develop (generate) a new

process plan• Generally requires a feature recognition system to identify a

compatible part family, then an expert system to step through the family process options

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Why CAPP?

Benefits of CAPP:• Reduces skill required of planner

• Reduces process planning time

• Reduces process planning & manufacturing costs

• Creates more consistent plans

• Produces more accurate plans

• Increases productivity!

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Where does this GT improved productivity impact the

Manufacturing Cost Breakdown

Fig. 2.5 Breakdown of costs for a manufactured product [Black, J T. (1991)]

Selling Price

15%5%

Eng’gManufacturing CostR & D

ProfitAdmin, Sales, Mktg, etc.

15% 25%40%

Mfg Cost

50%26%

Parts & Mat’ls Direct Labor

Plant / Mach. Depreciation,

Energy Indirect Labor

12%12%